We stayed at the Cavalieri in December, but the general distance is about the same. We pre-arranged for a car service (PM me if you want the link), and he was waiting for us when we arrived. About 40 euros; depends on how many bags you have. Very quick and direct -- the dispatcher speaks perfect English.

Likewise on our return, we called the same car service (an hour before we wanted to leave!) and they were waiting for us with a nice new black Mercedes. Same 40 euros.

In and around Rome, we pretty much walked everywhere -- central Rome is pretty compact.

Upon re-reading, I realize I was thinking you were arriving at FCO. Sorry